Navigation updating with FIX taking - question (pre GPS era testing)

[darkman222]

Question about FIX taking. How much can the INS drift in DCS in a regular mission. How is it possible that GPS is not available to take permanent care of INS drifting?

I did a travel of 350 nm with an airborne spawn F16 and the INS did not drift noticably.

The waypoint on the tip of the peninsula was more than good enough to kill a pre planned target here.

 

 

 

 

 

I am talking about that FIX taking turorial. When will that be necessary in DCS?

 

Edited June 8, 2023 by darkman222

[twistking]

I think you can disable GPS by selecting a date earlier than about 1980. Apart from that there is no use for fix taking that i'd know of.

[itn]

In leasurely cruise the drift is about under 1 NM/hr. My understanding is heavy maneuvering should cause more drift, but haven't tested it in DCS. Let us know if you test this with GPS disabled, heavy maneuvering, and say 1 hour of flight time. My guess is it's still around 0.8-1.0 NM/hr.

The GPS cutoff is in 1994 (March 28 1994 per some older forum post). So basically pre-1994 missions have no GPS available, unless "Unrestrictd SATNAV" is on. You could also just turn GPS off in plane.

If you have GPS available in mission and enabled in Viper, in practice it doesn't drift because of the constant GPS correction.

[darkman222]

I have now set the mission date to 1980. Time flown 35 minutes and 350 nm. The drift is not bad, but quite noticable. With some minor aerobatics too

So i guess for pre GPS missions kind of important, but for missions with GPS irrelevant. Correct me if I'm wrong.

Not really sure which waypoint is which, but my guess is that:

 

 

I might do another in depth test now as I can confirm that changing the date disables GPS and INS drift is modelled.

Edited June 7, 2023 by darkman222

[twistking]

with GPS not available, there would also be a reason to use offset aimpoints for targeting. if only they were not broken still...

by the way. what does change for the alignment process when GPS is not available?
do you need to enter coordinates manually for alignment? does stored heading align still function? anything else i should know when starting up the aircraft pre 1994?

Edited June 8, 2023 by twistking

[QuiGon]

14 hours ago, darkman222 said:

 So i guess for pre GPS missions kind of important, but for missions with GPS irrelevant. Correct me if I'm wrong.

That's exactly how it is. Fix taking was very important during the Cold War era, when there was no GPS. Flight planning for strike missions always included IP waypoints (preceeding the target point) on easily recognizable terrain features, to fix the nav system prior to attack to ensure precise weapon delivery.
Since the introduction of GPS this is no longer necessary. It's still being trained from time to time though, as in a peer to peer conflict, GPS might not be available or unreliable due to jamming/spoofing or GPS satelites getting shot down.

Edited June 8, 2023 by QuiGon

[darkman222]

To conclude my testing I have uploaded a short video.

Result: In MIZ pre GPS era INS drift is modelled. I will drift about 1100 ft per hour.

If you start up cold, ground aling, without entering coordinates, it will give perfect GPS alignment, which will start to drift over time too.

About the ground align without entering coordinates I am not sure, but the rest looks pretty realistic I would say.

 

[QuiGon]

4 hours ago, darkman222 said:

If you start up cold, ground aling, without entering coordinates, it will give perfect GPS alignment

That has nothing to do with GPS. The coordinates come from the data cartridge (or can be manually entered by the pilot on the INS page during the first ~2 minutes of alignment).

Edited June 23, 2023 by QuiGon

[darkman222]

Makes sense. Kind of. As I did not enter any coordinates , and we dont have the Catridge yet, I think DCS assumes there is a imaginary cartridge with the coordinates already inserted.

[QuiGon]

21 hours ago, darkman222 said:

Makes sense. Kind of. As I did not enter any coordinates , and we dont have the Catridge yet, I think DCS assumes there is a imaginary cartridge with the coordinates already inserted.

Yeah, that's how it works for now for most INS equipped aircraft in DCS.

[LastRifleRound]

Offsets would be more useful if they could be set in the ME. Entering in the aircraft, the precision isn't enough using the map tools to make it all that useful (like RAZBAM does with the Mirage, Harrier and F15E).